MCQ on Photosynthesis: Exercise with Answers

mcq on photosynthesis

Photosynthesis is a fundamental process for life on Earth, enabling plants, algae, and some bacteria to convert light energy into chemical energy. This process not only fuels the organism that performs it but also produces oxygen, which is essential for the survival of most living creatures. Understanding photosynthesis is crucial for students and professionals in biology, as it forms the basis of many ecological and physiological studies.

Multiple-choice questions (MCQs) are an effective tool for learning and evaluating knowledge on this topic. They help reinforce concepts and prepare students for exams. This article provides an overview of mcq on photosynthesis to test your understanding.

What is Photosynthesis?

Photosynthesis is a process by which green plants, algae, and some bacteria transform light energy, usually from the sun, into chemical energy stored in glucose. The basic chemical equation for photosynthesis is:

6CO2+6H2O+light energy→C6H12O6+6O26CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_26CO2​+6H2​O+light energy→C6​H12​O6​+6O2​

In this reaction, carbon dioxide (CO₂) and water (H₂O) are converted into glucose (C₆H₁₂O₆) and oxygen (O₂) using light energy absorbed by chlorophyll, the green pigment in plant leaves. This process occurs primarily in the chloroplasts, specifically within the thylakoid membranes.

Photosynthesis consists of two main stages: the light-dependent reactions and the Calvin cycle (light-independent reactions). During the light-dependent reactions, light energy is captured and used to produce ATP and NADPH, which are energy carriers. These reactions take place in the thylakoid membranes. In the Calvin cycle, which occurs in the stroma of the chloroplast, the energy from ATP and NADPH is used to convert carbon dioxide into glucose through a series of enzyme-mediated steps.

mcq on photosynthesis

Key Concepts in Photosynthesis

Light-dependent Reactions

Before going for practising some of the most common mcq on photosynthesis, let’s check out the details of the key concepts of photosynthesis. The light-dependent reactions are the initial phase of photosynthesis, taking place in the thylakoid membranes of the chloroplasts. These reactions require light to produce ATP and NADPH, which are essential for the subsequent steps in the Calvin cycle. The key events in the light-dependent reactions include the absorption of light by chlorophyll, the splitting of water molecules (photolysis), and the transfer of electrons through the electron transport chain.

  1. Photolysis: Water molecules are split into oxygen, protons, and electrons. This reaction is catalyzed by the enzyme complex located in the thylakoid membrane.
  2. Electron Transport Chain: Electrons excited by light energy travel through a series of proteins embedded in the thylakoid membrane, creating a proton gradient that drives the synthesis of ATP.
  3. ATP and NADPH Formation: The energy from the electron transport chain is used to convert ADP into ATP and NADP+ into NADPH.
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Calvin Cycle (Light-independent Reactions)

The Calvin cycle occurs in the stroma of the chloroplast and does not require light directly. Instead, it uses the ATP and NADPH produced in the light-dependent reactions to fix carbon dioxide into organic molecules. The key steps of the Calvin cycle include carbon fixation, reduction phase, and regeneration of ribulose-1,5-bisphosphate (RuBP).

  1. Carbon Fixation: CO₂ is attached to RuBP by the enzyme Rubisco, forming an unstable 6-carbon compound that quickly splits into two molecules of 3-phosphoglycerate (3-PGA).
  2. Reduction Phase: ATP and NADPH are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), a three-carbon sugar.
  3. Regeneration of RuBP: Some G3P molecules are used to regenerate RuBP, allowing the cycle to continue, while others are used to synthesize glucose and other carbohydrates.

Calvin Cycle

Common MCQ on photosynthesis

Sample MCQ on photosynthesis with answers

  1. What is the primary function of the light-dependent reactions?
    • a) Production of glucose
    • b) Carbon fixation
    • c) Production of ATP and NADPH
    • d) Release of oxygen
    • Answer: c) Production of ATP and NADPH
  2. Which gas is taken in by plants from the atmosphere during photosynthesis?
    • a) Nitrogen
    • b) Oxygen
    • c) Carbon dioxide
    • d) Hydrogen
    • Answer: c) Carbon dioxide
  3. Where does the Calvin cycle take place in the chloroplast?
    • a) Thylakoid membrane
    • b) Grana
    • c) Stroma
    • d) Outer membrane
    • Answer: c) Stroma
  4. Which color of light is least effective for photosynthesis?
    • a) Blue
    • b) Red
    • c) Green
    • d) Yellow
    • Answer: c) Green
  5. What is the optimum temperature for photosynthesis?
    • a) 10-15℃
    • b) 20-25℃
    • c) 25-35℃
    • d) 35-40℃
    • Answer: b) 20-25℃
  6. In which part of the chloroplast do the light-dependent reactions occur?
    • a) Stroma
    • b) Thylakoid membrane
    • c) Inner membrane
    • d) Outer membrane
    • Answer: b) Thylakoid membrane
  7. What is the primary pigment involved in photosynthesis?
    • a) Carotene
    • b) Xanthophyll
    • c) Chlorophyll
    • d) Anthocyanin
    • Answer: c) Chlorophyll
  8. Which molecule acts as an energy carrier in photosynthesis?
    • a) Glucose
    • b) NADPH
    • c) Oxygen
    • d) Water
    • Answer: b) NADPH
  9. What is the main product of the Calvin cycle?
    • a) Oxygen
    • b) ATP
    • c) NADPH
    • d) Glucose
    • Answer: d) Glucose
  10. Which enzyme is responsible for carbon fixation in the Calvin cycle?
    • a) Rubisco
    • b) ATP synthase
    • c) Cytochrome c
    • d) NADP reductase
    • Answer: a) Rubisco
  11. In what form do plants primarily store the energy produced in photosynthesis?
    • a) Starch
    • b) Protein
    • c) Lipids
    • d) Nucleic acids
    • Answer: a) Starch
  12. Which process in photosynthesis is responsible for producing oxygen?
    • a) Calvin cycle
    • b) Glycolysis
    • c) Photolysis of water
    • d) Krebs cycle
    • Answer: c) Photolysis of water
  13. Which component of the chloroplast is involved in the synthesis of ATP?
    • a) Stroma
    • b) Thylakoid membrane
    • c) Inner membrane
    • d) Outer membrane
    • Answer: b) Thylakoid membrane
  14. What is the first stable product of carbon fixation in the Calvin cycle?
    • a) RuBP
    • b) 3-PGA
    • c) G3P
    • d) NADPH
    • Answer: b) 3-PGA
  15. What happens to the oxygen produced during photosynthesis?
    • a) It is used in cellular respiration.
    • b) It is released into the atmosphere.
    • c) It is converted into glucose.
    • d) It remains in the chloroplast.
    • Answer: b) It is released into the atmosphere.
  16. Which factor can limit the rate of photosynthesis in plants?
    • a) Oxygen concentration
    • b) Carbon dioxide concentration
    • c) Nitrogen concentration
    • d) Chlorophyll concentration
    • Answer: b) Carbon dioxide concentration
  17. What role do stomata play in photosynthesis?
    • a) Absorb sunlight
    • b) Exchange gases
    • c) Transport water
    • d) Produce chlorophyll
    • Answer: b) Exchange gases
  18. What is the primary function of chlorophyll in photosynthesis?
    • a) Capture light energy
    • b) Transport electrons
    • c) Produce glucose
    • d) Store energy
    • Answer: a) Capture light energy
  19. Which molecule is regenerated during the Calvin cycle to keep the cycle going?
    • a) ATP
    • b) NADPH
    • c) RuBP
    • d) G3P
    • Answer: c) RuBP
  20. How many molecules of ATP are required to fix one molecule of CO₂ in the Calvin cycle?
    • a) 2
    • b) 3
    • c) 4
    • d) 6
    • Answer: b) 3
  21. What is the main purpose of the Calvin cycle?
    • a) To produce ATP
    • b) To fix carbon dioxide into glucose
    • c) To release oxygen
    • d) To absorb light energy
    • Answer: b) To fix carbon dioxide into glucose
  22. Which molecule is the primary acceptor of CO₂ in C4 plants?
    • a) RuBP
    • b) PEP (Phosphoenolpyruvate)
    • c) PGA
    • d) NADPH
    • Answer: b) PEP (Phosphoenolpyruvate)
  23. In which part of the leaf does most photosynthesis occur?
    • a) Epidermis
    • b) Mesophyll
    • c) Xylem
    • d) Phloem
    • Answer: b) Mesophyll
  24. Which process occurs during the light-dependent reactions?
    • a) Carbon fixation
    • b) Splitting of water
    • c) Glucose synthesis
    • d) Regeneration of RuBP
    • Answer: b) Splitting of water
  25. What is the main pigment involved in photosynthesis?
    • a) Carotenoids
    • b) Chlorophyll a
    • c) Anthocyanin
    • d) Xanthophyll
    • Answer: b) Chlorophyll a
  26. Which structure within the chloroplast is primarily responsible for the light-dependent reactions?
    • a) Stroma
    • b) Thylakoid membrane
    • c) Outer membrane
    • d) Inner membrane
    • Answer: b) Thylakoid membrane
  27. What happens to the electrons that are excited by light energy in photosystem II?
    • a) They are absorbed by chlorophyll a
    • b) They enter the electron transport chain
    • c) They split water molecules
    • d) They combine with oxygen
    • Answer: b) They enter the electron transport chain
  28. What is the final electron acceptor in the light-dependent reactions of photosynthesis?
    • a) Oxygen
    • b) NADP+
    • c) ADP
    • d) Water
    • Answer: b) NADP+
  29. Which enzyme is responsible for fixing CO₂ in the Calvin cycle?
    • a) ATP synthase
    • b) Rubisco
    • c) NADP reductase
    • d) Cytochrome c
    • Answer: b) Rubisco
  30. Which molecule is produced as a waste product in the light-dependent reactions?
    • a) Carbon dioxide
    • b) Water
    • c) Oxygen
    • d) Glucose
    • Answer: c) Oxygen
  31. How many turns of the Calvin cycle are required to produce one molecule of glucose?
    • a) Three
    • b) Six
    • c) Twelve
    • d) One
    • Answer: b) Six
  32. Which of the following is a product of the Calvin cycle?
    • a) ATP
    • b) NADPH
    • c) G3P (Glyceraldehyde-3-phosphate)
    • d) Oxygen
    • Answer: c) G3P (Glyceraldehyde-3-phosphate)
  33. Where are photosystems I and II located?
    • a) Stroma
    • b) Outer membrane
    • c) Thylakoid membrane
    • d) Cytoplasm
    • Answer: c) Thylakoid membrane
  34. Which light spectrum is most effective for photosynthesis?
    • a) Green
    • b) Yellow
    • c) Blue and red
    • d) UV
    • Answer: c) Blue and red
  35. What is the role of ATP synthase in photosynthesis?
    • a) Absorbing light
    • b) Synthesizing glucose
    • c) Producing ATP
    • d) Splitting water molecules
    • Answer: c) Producing ATP
  36. What is the function of the stomata in plant leaves?
    • a) Transporting water
    • b) Conducting photosynthesis
    • c) Gas exchange
    • d) Protecting from herbivores
    • Answer: c) Gas exchange
  37. What is photorespiration?
    • a) The process of capturing light energy
    • b) The conversion of carbon dioxide to glucose
    • c) A process where oxygen is consumed and carbon dioxide is released in the light
    • d) The production of ATP and NADPH
    • Answer: c) A process where oxygen is consumed and carbon dioxide is released in the light
  38. Which process uses carbon dioxide directly?
    • a) Light-dependent reactions
    • b) Electron transport chain
    • c) Calvin cycle
    • d) Photolysis
    • Answer: c) Calvin cycle
  39. Which compound is regenerated in the Calvin cycle to continue the cycle?
    • a) ATP
    • b) NADPH
    • c) RuBP
    • d) G3P
    • Answer: c) RuBP
  40. What is the main purpose of the light-dependent reactions?
    • a) To produce glucose
    • b) To produce oxygen
    • c) To convert light energy into chemical energy (ATP and NADPH)
    • d) To fix carbon dioxide
    • Answer: c) To convert light energy into chemical energy (ATP and NADPH)
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Common MCQ on photosynthesis

FAQs

Q1: Why is photosynthesis important? 

A: Photosynthesis is crucial because it converts solar energy into chemical energy, produces oxygen, and forms the base of the food chain.

Q2: Why is photosynthesis important? 

A: Photosynthesis is crucial because it converts solar energy into chemical energy stored in glucose, which plants use for growth and development. This process also produces oxygen as a byproduct, which is essential for the survival of most living organisms, including humans. Additionally, photosynthesis forms the foundation of the food chain, providing energy for herbivores, which in turn support carnivores.

Q3: What factors can limit the rate of photosynthesis? 

A: Factors that can limit the rate of photosynthesis include light intensity, carbon dioxide concentration, temperature, and water availability. Light intensity affects the energy supply for the light-dependent reactions. Carbon dioxide concentration influences the rate of carbon fixation in the Calvin cycle. Temperature affects enzyme activity, with extreme temperatures inhibiting photosynthesis. Water scarcity can limit the supply of electrons and protons needed for the light-dependent reactions.

Q4: What is the role of chlorophyll in photosynthesis? 

A: Chlorophyll is the primary pigment involved in photosynthesis. It absorbs light energy, predominantly in the blue and red wavelengths, and converts it into chemical energy. This energy is used to drive the light-dependent reactions, resulting in the production of ATP and NADPH, which are then utilized in the Calvin cycle to synthesize glucose.

Wrapping Up

Understanding photosynthesis is essential for comprehending how plants produce the energy necessary for their growth and development, as well as the oxygen vital for most life forms on Earth. By mastering the concepts and processes involved and exercising mcq on photosynthesis with their answers, you can gain insights into broader ecological and physiological phenomena. Practicing with multiple-choice questions helps reinforce this knowledge and prepares you for exams and practical applications. Keep studying, and don’t hesitate to explore additional resources to deepen your understanding of this vital biological process.